This invention relates to the field of glare reduction devices and other electronic vision devices. In particular, it relates to a method and apparatus for calibrating such a device to accommodate differences in facial geometry and other variations in the placement of a lens element of the device relative to the eye of a user.
When driving into the sun, the sun's glare frequently results in considerable discomfort to the driver. In some cases, the glare is so intense that the driver's pupils constrict to the point at which the rest of the field of view appears dark. This interruption in the driver's ability to see can arise without warning, for example when the driver turns a corner or goes around a bend, only to be greeted with the full force of the solar glare.
If the driver continues to drive, there is a significant risk of a collision arising from the driver's inability to see.
A personal glare reduction device has a lens medium that can be selectively darkened to at least partially cover a user's eye. Such a lens medium can, for example, employ the technology of an LCD display with individually addressable elements. A personal glare reduction device is typically coupled with a directional light sensor that determines the angular positions of bright light sources in the user's field of view. A processor obtains these angular positions and uses them to determine what points are to be darkened in order to prevent light from those light sources from reaching the user's eyes. The processor then automatically darkens the lens medium at those points through which light from the bright light sources passes on its way to the eye. This improves vision elsewhere in the user's field of view and reduces, if not eliminates, the onset of temporary blindness resulting from solar glare.
In order to locate the darkened portions of the lens medium correctly, it is desirable that a personal glare reduction device has accurate information as to the location of the lens element relative to the pupil of the user's eye. A common embodiment of a personal glare reduction device, which is one form of an electronic vision device according to the invention, is sunglasses, and other forms of eyeglasses. These embodiments have two optical windows, typically lens elements, one for each eye of the wearer. Because of both the natural variation in the way eyeglasses sit on people's faces and on the natural variations in eye spacing, it is desirable that a personal glare reduction device be provided with a calibration procedure. Such a calibration procedure is preferably intuitive and simple to perform.
U.S. Pat. No. 4,848,890 to Horn teaches a visor in which points on the visor are selectively darkened in response to the location of a light source. The Horn device includes a processor for identifying the angular location of a light source relative to the visor. In response to the angular location of the light source, the Horn device looks up a corresponding point or points in a look-up table, and darkens the visor at those points. However, no explicit means of adjustment is taught for calibrating the device to a particular user. Thus, in response to light incident from a particular angle, the Horn device darkens the same points on the visor without regard to any variations in the location of the visor relative to the user's pupil.
US Pat. No. 5,671,035 to Barnes teaches a light intensity reduction device containing a photosensitive element with a masking array to selectively darken output lenses for point-by-point light blocking. Barnes teaches a method for calibrating the device to an individual user by entering a programming mode in which the user manipulates a plurality of switches in an effort to direct a single darkened element on each lens to a position directly above the center of the eye.
One problem with the calibration method taught by Barnes is that it may be difficult for the user to determine exactly where the position directly above the center of the eye is. Even small errors in attempting to `look straight ahead,` or in perceiving the location of the darkened element, can lead to inaccurate calibration. In addition, the method taught by Barnes is time-consuming and requires that the user perform physically demanding tasks such as holding the head perfectly steady while attempting to adjust the location of a small darkened region or spot using controls with which, given the frequency of calibration, a user is unlikely to be familiar. The hand-eye coordination required to calibrate the Barnes device successfully is thus comparable to that required to do well in many video-games.
It is thus a purpose of the present invention to provide a quick, simple, and accurate method of calibrating a personal glare reduction device and other electronic vision devices, and to provide corresponding apparatus.
Other objects of the invention will in part be obvious and will in part appear hereinafter.